Johnny Mac also used it quite a bit, as did many of their era. Not as much power in the game back then tho'. The contact point for a Continental FH is usually a bit later than other strokes. This would tend to involve less body rotation to produce an efficient racquet head speed. This would generally mean that power is more difficult to produce on the FH with this grip.

I had always heard that the Eastern FH grip was inherently more powerful than other grips. However, since it does not easily produce as much topspin as the Western grips, it might not be easy to take advantage of that power without hitting the ball out.

Yes, for the amount of effort you put in, you can hit a ball that moves faster than eastern, SW, or full W.
But no, if you put in the effort to hit the other grips, you will hit with more power.
Yes, I said that, and you would need to think a bit before poo pooing....

There isn't really any DIRECT correlation between grip and power of the groundstroke. A flat stroke will put the most speed on the ball. You can hit flat with any grip. It may not be comfortable or as easy to hit a ball with a certain swingpath and impact location, but it can be done with any grip. It is easier to hit high balls with a western grip and low balls with a continental grip, but of course people with these grips can certainly hit either of these balls. A good player with any grip will be able to hit any ball in any way he chooses. You can hit huge topspin with a continental and can hit absoluely flat with a western grip, but it is less natural.

EFH would be the most powerful in general as it positions the hand/arm behind the racquet not on top which will encourage plow through.

the reason squash players use that grip is so they can use it for all shots, secondly the weight of the squash racquet means you can use your wrist more easily to generate racquet speed (also since you have less room you need to),

and of course, DEPENDS...
What do you mean by more powerful? Faster ball? more spin? Does more effort count? Is topspin the only thing you can think of?
More powerful...forehand. OK, EVERY pro, when they want to hit the ball as far as they can into the stands uses a continental grip! So is that more powerful? Nope, it only means hitting with backspin makes the ball go farther!
More powerful...forehand. If you are totally lacking in muscles to swing, a conti grip will allow you to hit the fastest moving forehand...it goes flat mostly, it scoops up low balls, and you can learn to slice it a bit to hit high balls far deep into the baseline.
And you use conti on serves, which I assume you'd want "power"....
:shock::shock:
The above is a one sided 30% answer to the question.

A continental is more adept at producing flatter balls from the same amount of effort from a player, and of course a flatter ball travels through the air quicker than a ball hit with the same force but with spin added.